Implications of ecological gradients and climate change on tree species composition, diversity and distribution in two eastern arc mountains, Tanzania

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Sokoine University of Agriculture.


The conservation of biological diversity in the tropics is important for improving ecosystem goods and services. Proper conservation planning however requires a thorough understanding of forest ecosystem processes that give rise to observed diversity and distribution patterns. Such knowledge may reflect underlying ecological processes that are important for management. Within forest ecosystems, plant communities have been associated with biotic and abiotic factors that often interact to form complex network of relationships. However, few attempts have addressed the questions of environmental effects to tree communities in the tropics with particular emphasis on the Eastern Arc Mountains (EAMs) of Tanzania. With recent environmental change, such ecosystems and component species are expected to respond uniquely, raising special conservation concerns. This study was carried out with the overall objective of determining tree species composition, diversity and distribution patterns in the Udzungwa (UMF) and East Usambara (EUF) Mountain forests of the EAMs as influenced by environmental gradients and climate change. Multivariate and Maximum Entropy Distribution Modelling (Maxent) was used in data analysis. High species richness was observed at mid-elevations suggesting that most of the species occur at moderate climatic conditions where growth and survival conditions are at optimal. There was a mixed response in species composition to mean annual temperature suggesting a heterogeneous effect of temperature on these two afromontane forests. The effects of edaphic factors appeared to be crucial in determining plant community patterns in the EAMs. Climatic and edaphic factors were predicted to be the main drivers of species distribution under current and future environmental conditions. Some species were predicted to lose their suitable habitats while others would gain through habitat (niche) expansion in response to climate change. Gradual variations in diversity responses to temperature for the two EAM sites suggest a need to focus on local patterns of climate change rather than broad-scale assessments. Conservation planners are advised to focus on local patterns of climate change and avoid broad-scale generalizations in assessment of how climate change might impact tree communities.



Biodiversity, Composition,, Climate change,, Climatic factors,, Ecological gradients,, Edaphic factors,, Eastern Arc Mountains